U.S. patent number 3,668,619 [Application Number 04/838,533] was granted by the patent office on 1972-06-06 for three-dimensional presentation of borehole logging data.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to Charles L. Dennis.
United States Patent |
3,668,619 |
Dennis |
June 6, 1972 |
THREE-DIMENSIONAL PRESENTATION OF BOREHOLE LOGGING DATA
Abstract
The specification discloses a technique and system for
recording, on a two-dimensional recording medium, data obtained
from cyclic scanning operations carried out angularly around the
wall of the borehole at each of a plurality of different depths
wherein subsurface parameters are sensed during each scanning
operation. In one embodiment, a plurality of loop-shaped trace
patterns, preferably in elliptical form, are recorded in the form
of a helix to form a representation of the borehole wall. Different
sides of the helix may be intensified or half sections of the helix
recorded to illustrate different sections of the borehole wall.
Inventors: |
Dennis; Charles L. (De Soto,
TX) |
Assignee: |
Mobil Oil Corporation
(N/A)
|
Family
ID: |
25277340 |
Appl.
No.: |
04/838,533 |
Filed: |
July 2, 1969 |
Current U.S.
Class: |
367/69; 367/25;
367/71; 315/391; 367/70; 367/72 |
Current CPC
Class: |
E21B
47/002 (20200501); G01V 1/44 (20130101); E21B
47/085 (20200501) |
Current International
Class: |
E21B
47/08 (20060101); E21B 47/00 (20060101); G01V
1/44 (20060101); G01V 1/40 (20060101); G01v
001/28 (); G01v 001/40 () |
Field of
Search: |
;343/7.9
;340/324.1,18,15.5BH ;315/18,22 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hubler; Malcolm F.
Claims
1. A method of recording data obtained from cyclic scanning
operations carried out angularly around the wall of a borehole at
each of a plurality of different depths wherein subsurface
parameters are sensed during each scanning cycle, comprising the
steps of:
producing two functions which are out of phase from each other and
are dependent upon the angular position at which scanning
operations are carried out during each cycle,
varying, as a function of said subsurface parameters sensed, the
tones of a trace pattern produced on a display medium of a display
system,
modifying at least one of said functions,
applying said two functions, at least one of which has been
modified, to said display system to produce an elliptical trace
pattern on said display medium for each scanning cycle, and
recording a plurality of said trace patterns on a two-dimensional
medium at successively displaced positions along a given direction
whereby a plurality of elliptical trace patterns are recorded to
form a helical
2. A system for recording data obtained from cyclic scanning
operations carried out angularly around the wall of a borehole at
each of a plurality of different depths wherein subsurface
parameters are sensed during each scanning operation,
comprising:
means for producing, on a display medium, a curved trace pattern
for each scanning cycle and having tones which are a function of
the borehole parameters sensed during each scanning cycle,
each trace pattern produced having the same scale, and
means for recording a plurality of said trace patterns on a
two-dimensional recording medium in the form of a helix to form a
representation of the
3. A system for recording data obtained from cyclic scanning
operations carried out angularly around the wall of a borehole at
each of a plurality of different depths wherein subsurface
parameters are sensed during each scanning cycle, comprising:
means for producing two functions which are out of phase from each
other and are dependent upon the angular position at which scanning
operations are carried out during each scanning cycle,
a display system including two deflection means for controlling the
movement of an electron beam with respect to a display medium and
electron beam modulating means,
means for applying one of said functions to one of said deflection
means and the other of said functions to the other of said
deflection means for cyclically producing a rotating beam sweep for
each scanning cycle,
means for varying the intensity of said electron beam as a function
of said subsurface parameters sensed during said scanning
operations for the production, on said medium, of a trace pattern
for each scanning cycle and having tones which are a function of
the borehole parameters sensed during each scanning cycle,
each trace pattern produced having the same scale, and
means for recording a plurality of said trace patterns on a
two-dimensional recording medium in the form of a helix to form a
representation of the
4. A method of recording data employing a display system having a
display medium and an electron beam producing means, said data
being obtained from cyclic scanning operations carried out from
within a borehole angularly around said borehole at each of a
plurality of different depths wherein subsurface parameters are
sensed during each scanning cycle, comprising the steps of:
producing a rotating electron beam sweep for each scanning cycle
for controlling the position of the electron beam when ON with
respect to said display medium,
each rotational electron beam sweep having the same scale,
within a predetermined angular portion of each rotational beam
sweep, varying the intensity of the electron beam as a function of
said subsurface parameters sensed over a corresponding portion of
each scanning cycle to cyclically display data, on said medium,
within said angular portion, and
on a two-dimensional recording medium, recording said displayed
data at
5. A method of recording data obtained from cyclic scanning
operations carried out angularly around the wall of a borehole at
each of a plurality of different depths wherein subsurface
parameters are sensed during each scanning cycle, comprising the
steps of:
producing, on a display medium, an arcuate trace pattern for each
scanning cycle and having tones which are a function of the
subsurface parameters sensed over a corresponding arcuate portion
of each scanning cycle,
each arcuate trace pattern produced having the same scale, and
recording a plurality of said arcuate trace patterns side by side
on a two-dimensional recording medium in the form of a portion of a
helix to
6. A method of recording data obtained from cyclical operations
carried out from within a borehole angularly around said borehole
at each of a plurality of different depths wherein subsurface
parameters are sensed during each scanning cycle, comprising the
steps of:
recording a plurality of l-op-shaped trace patterns on a
two-dimensional recording medium at successively displaced
positions along a given direction to form a representation of the
subsurface parameters sensed during a plurality of said scanning
cycles, each trace pattern having tones which are a function of the
subsurface parameters sensed during each scanning cycle, and
intensifying the tones of a predetermined arc of each loop-shaped
trace pattern compared to the tones of the remaining portion of
each loop-shaped pattern whereby the portion of said representation
formed by said arc of each loop-shaped trace pattern has an
intensity greater than the remaining
7. A method of recording data employing a display system having a
display medium and an electron beam producing means, said data
being obtained from cyclic scanning operations carried out
angularly around the wall of a borehole at each of a plurality of
different depths wherein subsurface parameters are sensed during
said scanning operations, comprising the steps of:
varying the intensity of the electron beam as a function of said
subsurface parameters sensed,
sweeping said electron beam when ON to form an arcuate trace
pattern on said display medium for each scanning cycle,
each arcuate trace pattern having the same scale, and
recording a plurality of said arcuate trace patterns side by side
on a two-dimensional recording medium to form a representation of a
portion of the wall of the borehole,
each arcuate trace pattern having tones which are a function of
the
8. A system for recording data obtained from cyclic scanning
operations carried out angularly around the wall of a borehole at
each of a plurality of different depths wherein subsurface
parameters are sensed during each scanning cycle, comprising:
a recording system including display means,
means for cyclically producing a pair of different arcuate trace
patterns t.sub.a and t.sub.b on said display means for each
scanning cycle,
said arcuate trace patterns t.sub.a and t .sub.b corresponding to
arcuate portions s.sub.a and s.sub.b, respectively, of each
scanning cycle,
said arcuate trace patterns t.sub.a and t.sub.b having tones which
are a function of the borehole parameters sensed over the
corresponding arcuate portions s.sub.a and s.sub.b, respectively,
during each scanning cycle, and
means for recording a plurality of said arcuate trace patterns
t.sub.a in side-by-side relationship and for recording a plurality
of said arcuate trace patterns t.sub.b in side-by-side relationship
to form two portions of a helix representative of separate portions
of the wall of the
9. A method of presenting data on display means of a display
system, said data being obtained from cyclic scanning operations
carried out angularly around the wall of a borehole at each of a
plurality of different depths wherein signals are produced which
are a function of subsurface parameters sensed during said scanning
operations, comprising the steps of:
applying said signals to said display system for cyclically
producing a pair of different arcuate trace patterns t.sub.a and
t.sub.b on said display means for each scanning cycle,
said arcuate trace patterns t.sub.a and t.sub.b corresponding to
arcuate portions s.sub.a and s.sub.b, respectively, of each
scanning cycle, said arcuate trace patterns t.sub.a and t.sub.b
having tones which are a function of the borehole parameters sensed
over the corresponding arcuate portions s.sub.a and s.sub.b,
respectively, during each scanning cycle, and
recording a plurality of said arcuate trace patterns t.sub.a in
side-by-side relationship and recording a plurality of said arcuate
trace patterns t.sub.b in side-by-side relationship to form two
portions of a helix representative of separate portions of the wall
of the borehole.
10. A system for recording data obtained from cyclic scanning
operations carried out from within a borehole angularly around said
borehole at each of a plurality of different depths wherein
subsurface parameters are sensed during said scanning operations,
comprising:
means for producing two functions which are out of phase from each
other and are dependent upon the angular position at which scanning
operations are carried out during each scanning cycle,
a display system including two deflection means for controlling the
movement of an electron beam with respect to a display medium and
electron beam modulating means,
means for applying one of said functions to one of said deflection
means and the other of said functions to the other of said
deflection means for cyclically producing a rotating electron beam
sweep for each scanning cycle,
means for applying to said modulating means, signals which are a
function of the subsurface parameters sensed, and
means for applying one of said functions to said modulating means
to control the level of the intensity of the electron beam during a
portion of each rotational beam sweep to cyclically display data on
said display
11. The system of claim 10 comprising:
means for recording on a two-dimensional recording medium said
displayed
12. A system for recording data obtained from cyclic scanning
operations carried out angularly around the wall of a borehole at
each of a plurality of different depths wherein subsurface
parameters are sensed during said scanning operations,
comprising:
means for producing sin and cos functions representative of the
angular position at which scanning operations are carried out
during each scanning cycle,
a display system including two deflection means for controlling the
movement of an electron beam with respect to a display medium and
electron beam modulating means,
means for applying said sin function to one of said deflection
means and said cos function to the other of said deflection means
for cyclically producing a loop-shaped beam sweep for each scanning
cycle,
means for applying to said modulating means, signals which are a
function of the subsurface parameters sensed, and
means for applying one of said functions to said modulating means
to control the level of the intensity of the electron beam during a
portion of each sweep cycle for the production of an arcuate trace
pattern on said medium which is a function of said borehole
parameters sensed during a
13. The system of claim 12 wherein said last-named means applies
said one of said functions to said modulating means to control the
level of the intensity of the electron beam during substantially
one half of each sweep cycle, said system comprising:
means for recording a plurality of said trace patterns side by side
on a two-dimensional recording medium in the form of substantially
one half of a cylindrical helix to form a representation of a
corresponding half
14. A system for recording data obtained form cyclic scanning
operations carried out angularly around the wall of a borehole at
each of a plurality of different depths wherein subsurface
parameters are sensed during said scanning operations,
comprising:
means for producing sin and cos functions representative of the
angular position at which scanning operations are carried out
during each scanning cycle,
a display system including two deflection means for controlling the
movement of an electron beam with respect to a display medium and
electron beam modulating means,
means for applying said sin function to one of said deflection
means and said cos function to the other of said deflection means
for cyclically producing a loop-shaped beam sweep for each scanning
cycle,
means for applying to said modulating means, signals which are a
function of said subsurface signals sensed,
means for forming the inverse of one of said functions, and
switching means for applying said one of said functions or said
inverse of said one of said functions to said modulating means to
control the level of the intensity of the electron beam during a
portion of each sweep cycle for the production of an arcuate trace
pattern on said medium which is a function of said borehole
parameter sensed during a corresponding arcuate
15. A system for recording data obtained from cyclic scanning
operations carried out angularly around the wall of a borehole at
each of a plurality of different depths wherein:
an energy transmitting and receiving means is rotated in said
borehole and operated periodically during each cycle to transmit
energy pulses to the borehole wall and to detect energy reflected
from said borehole wall, and
reflection signals are produced in response to reflected energy
detected, said system comprising:
a display device having a display medium and including deflection
means to control the movement of an electron beam,
modulating means for controlling the intensity of said electron
beam,
means for producing output pulses for each period of operation of
said transmitting and receiving means when reflection signals are
absent,
said output pulses being applied to said modulating means to
intensify said electron beam when reflection signals are absent,
and
control means for applying a control output to said deflection
means to produce a predetermined trace pattern on said display
medium for each
16. The system of claim 15 wherein:
said means for producing output pulses comprises a gate having two
inputs and an output,
said gate producing an output when the voltage levels at said two
inputs are at a predetermined value,
one of said inputs being biased normally to said predetermined
level,
means responsive to said reflection signals for producing
reflection-dependent waveforms at a level below said predetermined
value for application to said one input, and
means for applying gating pulses to said other input during a time
period when said waveforms are expected,
said gating pulses having a level at least as great as said
predetermined
17. The system of claim 15 wherein:
said control means produces two out-of-phase functions for each
scanning cycle for controlling the deflection of said electron beam
to produce a loop-shaped trace pattern on said display medium for
each scanning cycle.
18. The system of claim 17 comprising:
means for recording a plurality of said loop-shaped trace patterns
on a two-dimensional medium in the form of a helix to form a
representation of
19. A method of presenting data on a display medium of a display
system having an electron beam deflection means and an electron
beam modulating means, said data being obtained from cyclic
scanning operations carried out angularly around the wall of a
borehole at each of a plurality of different depths wherein:
an energy transmitting and receiving means is rotated in said
borehole and operated periodically during each cycle to transmit
energy pulses to the borehole wall and to detect energy reflected
from said borehole wall, and reflection signals are produced in
response to reflected energy detected, said method comprising the
steps of:
intensifying said electron beam when said reflection signals are
absent from said data, and
producing a predetermined electron beam sweep for each scanning
cycle to produce a predetermined trace pattern on said display
medium for each scanning cycle and having a high intensity
representative of the absence
20. The method of claim 19 comprising the steps of:
sweeping the electron beam when ON in an arcuate trace pattern for
each scanning cycle, and
recording a plurality of said arcuate trace patterns side by side
on a two-dimensional recording medium in the form of a portion of a
helix to
21. The method of claim 1 comprising the steps of: sweeping said
electron beam when ON to form a loop-shaped trace pattern on said
display medium for each scanning cycle, and
recording a plurality of said loop-shaped trace patterns in the
form of a helix on a two-dimensional recording medium to form a
representation of
22. A system for recording data obtained from cyclic scanning
operations carried out angularly around the wall of the borehole at
each of a plurality of different depths wherein:
an energy transmitting and receiving means is rotated in a borehole
and operated periodically during each cycle to transmit energy
pulses to the borehole wall and to detect energy reflected from
said borehole wall,
reflection signals are produced in response to reflected energy
detected, and
orienting pulses are produced each time said transmitting and
receiving means passes a predetermined geographic orientation, said
system comprising:
a display system including two deflection means for controlling the
movement of an electron beam with respect to a display medium and
an electron beam modulating means,
means responsive to each orienting pulse produced for generating
two out-of-phase waveforms for each scanning cycle,
one waveform having a period less than the period between
successive orienting pulses to obtain a quiescent interval between
successive waveforms,
the period of said interval being sufficient to allow a plurality
of said reflection signals to occur,
the other waveform function having a period substantially equal to
the period between successive orienting pulses,
means for applying said reflection signals to said modulating means
to intensify said beam with said reflection signals, and
means for applying one of said waveforms to one of said deflection
means and the other of said waveforms to the other of said
deflection means for cyclically producing a loop-shaped beam sweep
for each scanning cycle,
said interval resulting in said beam sweep being held at a given
position during the period of said interval to enhance the
production of an intensified spot at said position during each
cycle and representative of
23. The system of claim 22 wherein:
said two out-of-phase waveforms generated comprise a sin wave and a
cos wave,
said sin wave being generated to obtain said interval between
successive sin waves which is concomitant with the production of
each orienting
24. The system of claim 23 wherein said means for generating said
two out-of-phase waveforms comprises:
first means responsive to each orienting pulse produced for
generating said sin waveform, and
second means for integrating said sin waveform to generate said
cos
25. A system for recording data obtained from cyclic scanning
operations carried out angularly around the wall of a borehole at
each of a plurality of different depths wherein subsurface
parameters are sensed during said scanning operations,
comprising:
means for producing two out-of-phase functions which are dependent
upon the angular position at which scanning operations are carried
out during each cycle,
a display system having a display medium capable of displaying
color when irradiated with electrons,
said system having means for producing two electron beams and two
deflection means for deflecting said two electron beams,
means for applying to both of said electron beam producing means,
signals which are a function of said subsurface parameters
sensed,
means for applying one of said functions to one of said deflection
means and the other of said functions to the other of said
deflection means,
means for applying said one function to one of said electron beam
producing means and the inverse of said one function to the other
of said electron beam producing means for the production of a
loop-shaped trace pattern for each scanning cycle wherein one half
of said trace pattern is of one color and the other half of said
trace pattern is of another color.
Description
BACKGROUND OF THE INVENTION
This invention relates to a technique and recording system for
recording, on a two-dimensional medium, data obtained from borehole
scanning operations.
In U.S. Pat. No. 3,369,626, there is disclosed an acoustic borehole
logging technique and system wherein the walls of a borehole are
scanned periodically with acoustic energy for obtaining information
of interest. In one embodiment, a single transducer which acts both
as a transmitter and receiver is rotated in the borehole and
periodically actuated to produce acoustic pulses which are applied
to the borehole wall. Reflected energy is detected by the
transducer between acoustic pulses and converted into signals which
are employed to intensity modulate the electron beam of an
oscilloscope. The beam in one embodiment may be swept linearly
across the screen of the oscilloscope once for each rotation of the
transducer. Successive traces are recorded side by side in row
fashion to obtain a folded-out section of the borehole wall. In
another embodiment, a PPI presentation is obtained wherein circular
traces of diminishing diameter are produced and recorded within
each other.
U.S. Pat. No. 3,434,568 discloses that the folded-out section may
be produced on a transparency and folded into a cylinder to aid in
interpretation.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a
unique technique and system for presenting and recording, on a
two-dimensional recording medium, data obtained from cyclic
scanning operations carried out from within a borehole angularly
around the borehole at each of a plurality of different depths
wherein subsurface parameters are sensed during each scanning
operation. In carrying out the invention, data may be angularly
recorded on the recording medium at successively displaced
positions around a moving or successively displaced center. In one
embodiment, a plurality of loop-shaped trace patterns are recorded
on the recording medium in the form of a helix to form a
representation of the wall of the borehole. The loop-shaped trace
patterns produced preferably are in elliptical form and have tones
which are a function of the borehole parameters sensed during each
scanning cycle. The scanning operations may be carried out to
obtain a record of the fractures in the borehole wall. These
fractures may be illustrated in darker tones on a lighter
background or in lighter tones on a darker background.
The borehole system disclosed comprises an acoustic transducing
means which is rotated and periodically operated to transmit
acoustic pulses to the borehole wall. The transducing means detects
reflected energy for the production of reflection signals. During
logging operations, an orientation signal or a cyclic control
signal is produced each time the transducing means is rotated past
a predetermined geographic orientation or at the beginning of each
cycle of rotation, respectively. Either of these signals may be
employed to produce two out-of-phase functions which are dependent
upon the angular position at which scanning operations are carried
out during each scanning cycle. The recording system comprises a
display system having a display medium, two electron beam
deflection means, and an electron beam intensity modulating means.
The two out-of-phase functions are applied to the two deflection
means respectively to cyclically produce a loop-shaped or rotating
beam sweep. In one embodiment, the reflection signals are applied
to the electron beam modulating means to intensify the beam whereby
fractures (which result in the lack of reflection signals) are
illustrated on the display medium in darker tones on a lighter
background. In another embodiment, the reflection signals are
applied to a circuit for the production of output signals when
reflection signals (hence fractures) are absent. These output
signals are applied to the electron beam modulating means to
intensify the beam whereby fractures are illustrated on the display
medium in lighter tones on a darker background.
In another embodiment, different sides of the helix produced may be
intensified or half sections of the helix recorded to illustrate
different sections of the borehole wall around its axis. These
outputs are produced by applying one of the two out-of-phase
functions to the electron beam modulating means whereby it is mixed
with the reflection signals or output signals applied thereto. The
electron beam is intensified during a particular half cycle of the
beam sweep depending upon the polarity of the out-of-phase function
and the reflection or output signals applied to the electron beam
modulating means. Opposite half cycles may be intensified by
inverting the out-of-phase function before application to the
electron beam modulating means. Two half sections of the helix may
be produced simultaneously by employing a display system having two
electron guns. One of the out-of-phase functions is applied to the
electron beam modulation means of one gun and inverted and applied
to the electron beam modulation means of the other gun.
In open-hole logging, the orienting pulses are employed to produce
the two out-of-phase functions which are disclosed as sin and cos
waveforms. The function-producing system disclosed produces a sin
waveform from which the cos waveform is derived. The period of the
sin waveform is slightly less than the period of each downhole
scanning cycle. The interval between successive sin waveforms
occurs at a predetermined geographic orientation and is sufficient
in time to allow a plurality of reflection signals to occur. This
interval causes the beam sweep to be held at a given position
during the period of the interval to enhance the production of an
intensified spot on the display medium at this position during each
cycle and representative of geographic orientation. Hence, as
successive trace patterns are recorded, an intensified line,
running in the direction of depth, is produced which represents a
predetermined geographic orientation.
In another embodiment, each trace pattern reflects caliper
information representative of variations in the distance between
the transducing means and the wall of the borehole. In the
embodiment disclosed, the caliper information is obtained by
producing a caliper function which is dependent upon the distance
between the transducing means and the wall of the borehole. This
caliper function is combined with each of the two out-of-phase
functions which then are applied to the electron beam deflection
means to produce a curved electron beam sweep having excursions
which are representative of variations in the distance between the
transducing means and the wall of the borehole.
In a further embodiment, a display system is employed which has two
electron beam producing means and also has a display medium capable
of displaying color when irradiated with electrons. This system has
two deflection means for deflecting the two electron beams. The
reflection signals or output signals are applied to both of the
electron beam producing means while one of the out-of-phase
functions is applied to one deflection means and the other of the
out-of-phase functions is applied to the other deflection means. In
addition, one of the out-of-phase functions is mixed with the
reflection signals or the output signals and applied to intensity
modulate one electron beam. This function also is inverted and
mixed with the reflection signals or output signals and employed to
intensity modulate the other electron beam. A loop-shaped trace
pattern is produced for each scanning cycle wherein one half of the
trace pattern is of one color and the other half of the trace
pattern is of another color. The use of different colors may be
employed to aid in the interpretation of the record obtained.
The present invention may be employed to define the wall of a
borehole or to obtain a display of subsurface parameters within the
formations around the borehole. In this latter embodiment, an
energy transmitting and receiving means is rotated in the borehole
and operated to transmit energy pulses into the formations and to
detect reflected energy. The electron beam of the display system is
swept in a PPI scan for each downhole scanning cycle and modulated
with signals formed from reflected energy detected. The display
obtained for each scanning cycle is recorded on a two-dimensional
recording medium in a helical manner to form the desired
representation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates one embodiment of the present invention employed
in combination with an acoustic well logging system;
FIG. 2 is a helical display of the borehole as obtained with the
system of FIG. 1;
FIGS. 3A-3F and 4 are traces useful in understanding the system of
FIG. 1;
FIG. 5 is a helical display with a magnetic north line formed on
the backside;
FIG. 6 is a helical display having tones which are the inverse of
those of FIG. 2;
FIG. 7 illustrates the system employed for obtaining the display of
FIG. 6;
FIGS. 8A-8E illustrate traces useful in understanding the system of
FIG. 7;
FIG. 9 illustrates two half sections of the display of FIG. 2;
FIG. 10 illustrates circuitry employed for obtaining the display of
FIG. 9;
FIGS. 11A and 11B illustrate traces useful in understanding the
circuitry of FIG. 10;
FIG. 12 is a helical display of a borehole model with one side
intensified;
FIG. 13 is a system for producing and recording simultaneously the
two presentations of FIG. 12;
FIG. 14 is a system for incorporating caliper information on the
trace patterns obtained;
FIGS. 15 and 16A-16E illustrate traces useful in understanding the
system of FIG. 14;
FIG. 17 illustrates a system for obtaining trace patterns with half
sections of different color;
FIG. 18 illustrates a dual transducer system for investigating the
subsurface formations;
FIG. 19 is a presentation of reflecting surfaces or interfaces
extending into the formations from the borehole wall;
FIG. 20 illustrates circuitry for obtaining the presentation of
FIG. 19;
FIGS. 21A and 21B and FIGS. 22A-22D are traces useful in
understanding the circuitry of FIG. 20;
FIG. 23 illustrates an alternative system for recording the trace
patterns or data obtained;
FIGS. 24 and 25 illustrate in more detail the rotating switch and
the gate-detector circuitry employed in the downhole tool of FIG.
1; and
FIG. 26 illustrates in more detail the uphole circuitry of FIG. 1
for separating the sync pulses and receiver signals.
DESCRIPTION OF THE BOREHOLE SYSTEM
Referring now to FIG. 1, there will be described briefly a borehole
system employed for carrying out logging operations in a borehole
illustrated at 30 and containing borehole fluid 31. The borehole
logging system comprises a borehole tool 32 having located therein
an acoustic transducer 33 which acts as a transmitter and receiver
of acoustic energy. During logging operations, the transducer 33 is
rotated through 360.degree. by motor 34, mechanical drive 35
(illustrated in detail in U.S. Pat. No. 3,378,097,) sleeve 36, and
transducer mount 37. The sleeve 36 rotates about mandrel 38 which
connects end member 39 to structure 40. In one embodiment, the
transducer is rotated at a rate of about 180 revolutions per
minute. During each 360.degree. cycle, the transducer 33 is pulsed
periodically, in one embodiment, at a rate of about 2,000 pulses
per second for the application of acoustic pulses to the borehole
wall by way of tool fluid 41, rubber boot 42, and the borehole
fluid 31. The predominant frequency of the acoustic pulses may be
of the order of 1.35 megacycles. Pulse generator 44 which is
coupled to transducer 33 by way of conductor 45 and slip rings (not
shown) periodically actuates the transducer for the production of
acoustic pulses. Between transmitted acoustic pulses, reflected
energy is detected by the transducer 33 and applied to the surface
by way of conductor 45; amplifier, gate, and detector system 46;
and cable conductor 47. Synch pulses are obtained from the
transducer 33, when it is actuated, and also are applied to
conductor 47 for transmission to the surface.
Coupled to mechanical drive 35 for rotation therewith is a magnetic
north sensing means 50 which in turn is coupled to circuitry 51
which produces an orienting signal each time the transducer 33
passes magnetic north. Also coupled to the mechanical drive 35 for
rotation therewith is an arm 54 which cyclically contacts terminal
55 of a rotating switching system 56. A cyclic pulse is produced
each time the arm 54 contacts terminal 55. A downhole switching
system controlled from the surface is employed to transmit either
the orienting signals or the cyclic pulses uphole. For ease of
illustration, the switching system is shown as located uphole and
separate cable conductors are disclosed for transmitting the
orienting signals and the cyclic pulses to the surface. These cable
conductors are illustrated at 60 and 61, respectively.
During logging operations, drum 70, driven by motor 71 and
connection 72, winds and unwinds the supporting cable 73 to move
the tool 32 continuously through the borehole. At the surface, the
various pulses and signals are taken from the cable conductors by
way of slip rings and brushes illustrated, respectively, at 74 and
75.
The sync pulses and the reflection signals are applied by way of
conductor 47' to the circuitry 76 where the reflection signals are
separated and applied by way of conductor 77 to the recording
system. An uphole switch 78 is employed to select either the
orienting pulses or the cyclic pulses from conductors 60' or 61',
respectively. The signals or pulses selected then are amplified at
79 and employed for obtaining the desired presentations. For
open-hole logging, the orienting pulses are used while the cyclic
pulses from the rotating switch 56 are used in casing
inspection.
DESCRIPTION OF THE PRESENT INVENTION
The system illustrated in FIG. 1 is an on-line system for obtaining
the desired presentations while logging; however, it is to be
understood that the borehole data may be recorded on magnetic tape
and subsequently played back to obtain the desired
presentations.
In the system of FIG. 1, the reflection signals are applied by way
of conductor 77 to the Z-axis circuit 80 of a standard,
commercially available oscilloscope 81 to intensity modulate the
electron beam of the scope. For open-hole logging, orienting pulses
are selected and employed to derive two out-of-phase waveform
functions. These waveforms are applied, respectively, to the
vertical deflecting means 82 and to the horizontal deflecting means
83 of the scope to produce a rotating or loop-shaped beam sweep
once for each scanning cycle of the transducer 33. Hence, a
loop-shaped trace pattern shown in solid line 84 is produced on the
screen 85 of the scope for each downhole scanning cycle. Successive
trace patterns are recorded, by a recording means, in helical form
to obtain a three-dimensional presentation or effect which is
representative of the wall of the borehole. Such a presentation is
illustrated at 90 in FIG. 2. In obtaining this presentation, the
reflection signals intensify the electron beam whereby reflected
energy detected is presented in lighter tones on the screen 85,
while fractures or the lack of reflection signals are presented in
darker tones. The oblique elliptical pattern 91 represents an
oblique fracture in the formations which crosses the borehole
logged.
In the following description, it is to be understood that the tones
of the presentations of FIGS. 2, 5, 6, 9, and 12 are the inverse of
those displayed on the screen of a cathode-ray tube of the display
system. These presentations are employed in this application to
facilitate printing. They were produced from positive
transparencies obtained from Polaroid prints made of the displays
produced on the screen of the display system.
As now can be understood from the presentation of FIG. 2, the
technique and system of the present invention allows one to obtain
a three-dimensional effect of the borehole wall which may be
obtained very readily by electronic means and which is very useful
in interpretation purposes. In addition, the present invention
allows one to obtain the presentations continuously over the entire
length of the borehole.
Referring to FIGS. 1, 3, and 4, there will be described in more
detail the system and technique for obtaining the presentation of
FIG. 2. In this respect, FIGS. 3B and 3C have a greatly expanded
time scale relative to FIGS. 3A and 3D-3F. The pulses at 92 in FIG.
3A represent the orientation or cyclic control pulses, which occur
once for each 360.degree. rotating or scanning cycle of the
transducer 33. If the transducer is rotated at a speed of 180
revolutions per minute, the orienting or cyclic control pulses
occur at a rate of 3 per second. In FIG. 3B, pulses 93 and 94
illustrate sync pulses and the output of the transducer,
respectively, as it detects acoustic energy reflected from the
borehole wall. The downhole circuitry 46, FIG. 1, detects the
resulting pulses to form the envelope signals 93a and 94a for
transmission to the surface. Since the transducer is pulsed at a
repetition rate of about 2,000 pulses per second, a large number of
sync pulses and reflection signals are produced during each
rotating or scanning cycle of the transducer 33. At the surface,
the reflection signals 94a are passed by the circuitry 76 to the
Z-axis circuitry 80 of the oscilloscope 81. Application of these
signals to the Z axis is by way of input 80a and capacitor 80b.
These signals may be employed to control either the cathode or the
grid of the cathode-ray tube of the oscilloscope to intensity
modulate the electron beam. In the systems shown, the cathode will
be described as being controlled for intensity modulation purposes.
In this respect, the negative signals 94a, when applied to the
cathode, intensify the electron beam.
The arrangement for producing the two out-of-phase functions
comprises a variable diode function generator 100 having a
frequency control dial 101. The pulses from amplifier 79 trigger
the function generator 100 which produces a sin wave when
triggered. Dial 101 may be adjusted whereby the period of each sin
wave is the same as the period of each scanning cycle of the
transducer 33 or it may be adjusted to decrease or increase the
period of the sin wave. In the present system, it is desirable that
the period of each sin wave produced be slightly less than the
period of each downhole scanning cycle in order to provide an
interval between sin waves which will allow for drift of the
downhole motor 34 or for drift of the variable diode function
generator 100 to take place without affecting the stability of the
trace patterns 84. In FIG. 3D, the sin wave generated in response
to each trigger pulse applied from amplifier 79 is illustrated at
103. As can be seen, the period of the sin wave 103 is slightly
less than the period between successive pulses 92 which define each
downhole scanning cycle. The time interval 104 is the safety time
factor between sin waves as mentioned above. The output of the
function generator 100 is integrated at 105 and inverted for the
production of a cos wave illustrated at 106 in FIG. 3E. Integrator
105 acts as a low-pass filter to smooth the sin wave 103 whereby
the cos wave 106 has a period equal to the period between
successive pulses 92. The output of integrator 105 is applied by
way of input adder 107a to the vertical deflection amplifier 107 of
the oscilloscope 81 and also to a second integrator 108. Integrator
108 converts the cos wave 106 to a sin wave illustrated in FIG. 3F
at 109. This sin wave is then applied by way of input 110a to the
horizontal deflection amplifier 110. Gain controls 111 and 112 are
adjusted to obtain the desired form of the trace pattern 84. In the
preferred embodiment, as mentioned above, the trace pattern is an
ellipse. This is obtained by adjusting the control 111 to obtain a
gain for the vertical deflection means of one half that applied to
the horizontal deflection means. Other suitable vertical-horizontal
gain ratios may be employed. FIG. 4 illustrates the cos and sin
waveforms applied to the vertical and horizontal deflection means
to produce the trace pattern 84. In the preferred embodiment, the
scope 81 is of the type having electrostatic deflection plates 82
and 83; however, magnetic deflection means could be employed.
In the system disclosed, the beam spot on the screen and hence each
trace pattern 84 begins at a point 113 above its center 114 for
each cycle and moves clockwise to form each elliptical trace
pattern 84. The clockwise movement of the beam spot to form the
trace pattern 84 is desired since the downhole motor 34 is driven
in a manner to rotate the transducer 33 clockwise around the
mandrel 38.
In obtaining a record of a plurality of successive patterns 84 in
side-by-side relationship to form the helical presentation of FIG.
2, successive trace patterns 84 may be stepped vertically and
photographed by a camera 115 employing film, for example,
manufactured by Polaroid. In the alternative, successive trace
patterns 84 may be produced at the same position on the screen 85
and a camera employed having a film continuously driven in
correlation with the movement of the tool 32. The first embodiment
will be described in connection with FIG. 1. However, it is to be
understood that either photographing techniques or systems may be
employed with any of the embodiments of the present invention.
The system for vertically stepping the trace patterns 84 produced
for each scanning cycle of the transducer 33 comprises a
potentiometer 116, the arm 117 of which is mechanically coupled
through gear reducer 118 to reel 119 driven by the logging cable
73. As the cable 73 is moved continuously to move the tool 32
through the borehole, the arm 117 of the potentiometer 116 moves
across the resistive element 120, thereby generating a slowly
changing voltage which is applied to the vertical deflection plates
82 by way of adder 107a and vertical deflection amplifier 107.
Since the tool 32 is moved upward through the borehole when logging
operations are carried out, the polarity of the voltage obtained
from potentiometer 116 changes in a direction to slowly displace
each trace pattern in the upward direction. Thus, data is presented
by the beam spot on the screen around a center point which is
successively displaced upward. Displacement between the beginning
and ending of each beam sweep may be of the order of one beam spot
width. The dotted line 84' in FIG. 1 illustrates a trace pattern
produced subsequent to the production of the preceding pattern 84.
As now can be understood, a cylindrical helix is formed as each
trace pattern is recorded at successively displaced positions on
film.
In open-hole logging, since each trace pattern is initiated by the
orienting pulse, the interpreter knows that the beginning point 113
of each trace pattern indicates magnetic north. Hence, in the
presentation of FIG. 2, an imaginary vertical line on the backside
of the helical figure about midway between the two vertical edges
of the helical presentation represents magnetic north.
If desired, this magnetic north line may be incorporated in the
helical presentation of the borehole. FIG. 5 illustrates a helical
presentation having such a magnetic north line 123 formed on the
backside of the helix. This line may be formed by taking the output
of the function generator 100, which is the waveform 103 of FIG.
3D, and applying it, rather than the output of integrator 108, to
the horizontal deflection plates 83. This may be done by opening
switch 126 and closing switch 127. With this arrangement, the time
interval or step 104 between sin waveforms 103 will result in the
beam sweep being held at the upper position 113 for a period of
time which is sufficient to allow the transducer 33 to be pulsed a
plurality of times. The period 104 in one embodiment may be of the
order of 5 to 10 milliseconds. During this time if the transducer
33 is passing a reflecting surface, reflection signals will be
produced which will intensify the trace at point 113 on the screen
of the scope. The step period 104 produced during each trace cycle
hence enhances the probability that reflection signals will
intensify the electron beam at point 113 during each sweep cycle,
thereby resulting in the production of the magnetic north line 123
on the presentation of FIG. 5.
In order to obtain three-dimensional figures of the borehole which
enhance the presentation of fractures in the formations, the system
may be modified to intensify the electron beam when reflection
signals are absent whereby fractures are presented in lighter tones
on a darker background on the screen of the scope. Enhancement of
the presentation of fractures is obtained since generally there are
more reflecting surface areas around the wall of the borehole than
there are nonreflecting areas where fractures are present. Thus,
there is more background than information of interest. By
emphasizing this information rather than the background, the
fractures will stand out against the background. A
three-dimensional presentation obtained by intensifying the
electron beam when reflection signals are absent is shown at 90' in
FIG. 6. As indicated previously, the tones of this presentation are
the inverse of those displayed on the screen of the scope. This
presentation represents the same borehole section as does FIG. 2
but at a different viewpoint. As can be seen, the fracture 91' is
very prominently illustrated.
Referring now to FIGS. 7 and 8, there will be described the
circuitry for producing the display from which FIG. 6 was obtained.
This system comprises clamping diodes 130 and 131 which form an AND
gate with one input variable complemented. A reflection-dependent
waveform is applied to the input 132 of diode 130 when reflection
signals are received. In addition, an auxiliary or gating pulse is
applied to the input 133 of diode 131 during each operating period
of the downhole transducer 33. This auxiliary or gating pulse
occurs slightly after the leading edge of the reflection-dependent
waveform is expected. The magnitude of the auxiliary pulses is
constant while the magnitude of the reflection-dependent waveforms,
when they occur, is dependent upon the magnitude of the reflection
signals. When a full magnitude reflection signal occurs, no output
signal is produced at the output 134 whereby the electron beam of
the oscilloscope is not intensified. As the magnitude of the
reflection signals decreases in absolute value, the output signals
at 134 increase whereby the electron beam is intensified at
increasingly higher levels. When no reflection signal occurs, the
output at 134 is at a maximum and the electron beam is intensified
to its highest level. Thus, reflecting surfaces of the borehole
wall will be presented on the screen in darker tones; and
fractures, which result in the lack of reflection signals, will be
presented in lighter tones.
The gating pulse applied to input 133 is generated in response to
each sync pulse which is obtained from the circuitry 76 of FIG. 1.
The synch pulses are illustrated at 93a in FIG. 8 and are applied
by way of conductor 135 to a pulse generator 136 for the generation
of the gating pulses, one of which is illustrated at 138 in FIG.
8B. FIG. 8C illustrates a reflection signal 94a obtained from
conductor 77 of FIG. 1. Delay control 139 is adjusted whereby the
gating pulses 138 begin at a time shortly after the time that the
reflection signals are expected. The time between the end of a
reflection signal and the beginning of a gating pulse for a given
borehole size and caliper variation may be of the order of 50
microseconds. Pulse width control 140 is adjusted whereby the width
of the pulse 138 may be greater than the width of the reflection
signal 94a. Each gating pulse 138 has an amplitude of 30 volts.
Transistor 141 is employed to ensure that each gating pulse has a
base level of 0 volts.
In obtaining the display from which the presentation of FIG. 6 was
produced, the conductor 77 of FIG. 1 is coupled to the
potentiometer 142 rather than directly to the Z axis of the
oscilloscope. The purpose of the potentiometer 142 is to ensure
that the largest received echo will result in a -30 volt reflection
signal from a base level of zero. In this respect, the adjustment
may be carried out with the aid of a monitor scope whose vertical
deflection plates are coupled to the output of potentiometer 142
and whose electron beam is swept across the screen once for each
sync pulse.
Resistor 145, capacitor 146, and the internal resistance of
transistor 147 convert the reflection signal 94a into an inverted
sawtooth waveform 148 (FIG. 8D) which has a slow rise time. Thus,
even though the reflection signal 94a and hence the waveform 148
begin prior to the occurrence of the gating pulse 138, a portion of
the waveform 148 will occur coincidentally with the occurrence of
gating pulse 138. In one embodiment, the resistive and capacitive
parameters are selected whereby the waveform 148 has a time
constant of about 240 microseconds. The period of the gating pulse
138 may be of the order of 20 microseconds.
Transistor 147 also is employed to shift the base line of the
waveform 148 from 0 volts to 30 volts. When no reflection signal is
present, waveform 148 will not be produced and the gate comprising
diodes 130 and 131 will produce an output signal of 30 volts at 134
when the gating pulse is applied to the input 133. These output
signals are inverted by transistor 149 for application to the Z
axis to intensify the electron beam of the oscilloscope. When a
full magnitude reflection echo is received by the transducer, the
waveform 148 will have a peak value of 0 volts and no output will
be produced at 134 whereby the electron beam will not be
intensified. If the echo received has an intermediate value, the
waveform 148 will have a peak value, for example, of 15 volts and
the output at 134 will be a signal of 15 volts whereby the electron
beam will be intensified to an intermediate level.
FIG. 8E illustrates the form of the output at 134 when a reflection
signal of intermediate level is produced.
In obtaining the presentation of FIG. 6, it will be understood that
the cos waveform from integrator 105 and the sin waveform from
integrator 108 will be applied by way of amplifiers 107 and 110 to
the vertical and horizontal deflection plates 82 and 83,
respectively, of the scope 81 to obtain the elliptical trace
patterns. The output from potentiometer 116 may be applied to the
vertical plates for vertically stepping the elliptical trace
patterns. Camera 115 may be employed to photograph successive trace
patterns to obtain the presentation of FIG. 6.
In some instances, it may be desirable to present the general
outline of the borehole in gray with fractures shown in lighter
tones on the screen of the scope. The gray outline may be obtained
by the following adjustment procedure. First, the external input to
the Z axis of the scope is removed while the sin and cos waveforms
are applied to the deflection plates. The intensity control
illustrated at 150 in FIG. 7 is adjusted in order to obtain a trace
pattern of very low intensity. The external Z-axis input is
reconnected and then potentiometer 151 is controlled to adjust the
intensity of the electron beam to the highest desired level when no
reflection-dependent waveforms are applied to the input 132 of the
gating system but while auxiliary pulses are applied to the input
at 133.
Although the circuitry of FIG. 7 was disclosed for producing the
helical figures, it is to be understood that it has other uses. For
example, it could be used in the production of the flat, folded-out
sections described in U.S. Pat. No. 3,369,626.
In a further embodiment, the helical presentations of the present
invention may be shown in cross section through the axis of the
helical figures in order to display different angular sections of
the borehole for better analysis and interpretation. The
presentations 90a and 90b of FIG. 9 are the frontside and backside,
respectively, of the helical configuration 90 of FIG. 2. The
sectional presentations of FIG. 9 have advantages in that there is
no overlapping of frontside traces with the backside traces and
hence the presentations more clearly show the corresponding
sections of the borehole. Each section of FIG. 9 may be recorded
separately or simultaneously.
FIG. 10 illustrates a system for recording each section separately.
This system includes the oscilloscope 81 having certain components
shown in more detail but with other components such as the
amplifiers 107 and 110 omitted for clarity. The sin and cos
functions are applied to the horizontal and vertical deflection
plates 83 and 82, respectively, while the reflection signals are
applied to the Z input 80a as described in connection with FIG. 1.
In order to obtain the desired sectional half of the borehole,
either the sin or cos function or the inverse thereof is mixed with
the reflection signals. The frontside of FIG. 9 is obtained by
mixing the cos function with the reflection signals. The
positive-going portions of the cos waveform mixed with the
reflection signals occur during the production of the backside beam
sweep. This can be understood by reference to FIG. 4. These
positive-going portions, shown in FIG. 11A, in effect, cancel out
the negative reflection signals. Hence, during the occurrence of
the backside beam sweep, the electron beam will not be intensified
by reflection signals and the backside of each trace pattern will
be dark. During the time that the frontside beam sweep is being
produced, the negative-going portions of the cos waveform will
reinforce the negative reflection signals whereby the frontside
trace pattern will be produced.
The backside presentation is obtained by mixing the inverse of the
cos function with the reflection signals. The inverse of the cos
waveform is shown in FIG. 11B. As now can be understood, the
positive-going portions of the inverse occur during the frontside
beam sweep and the negative-going portion occurs during the
backside beam sweep whereby the frontside trace pattern on the
screen of the scope will be dark while the backside trace pattern
will be light.
In order to obtain the frontside presentation, switch 160 of FIG.
10 is moved to contact terminal 161. The cos function then is
applied to the Z axis of the scope 81 by way of potentiometer 162,
terminal 161, switch 160, and resistor 163. The reflection signals
are applied to the Z axis by way of potentiometer 164 and capacitor
80b. Capacitor 80b and resistor 163 act as a mixer. The cos
function and the reflection signals thus are mixed at the juncture
165 and applied to the cathode circuit 80.
Potentiometer 162 is employed to control the amplitude of the
waveform mixed with the reflection signals. Potentiometer 164 is
employed to control the amplitude of the reflection signals, while
potentiometer or intensity control 150 is employed to control the
threshold or intensity level of the electron beam. These three
potentiometers are adjusted to obtain the desired trace pattern.
For example, in obtaining the frontside presentation,
potentiometers 162 and 164 initially are adjusted to positions to
bias out the amplitude of the cos waveform and the reflection
signals whereby the cos waveform and reflection signals are, in
effect, removed from the Z axis. While the cos waveform and sin
waveform are being applied to the vertical and horizontal
deflection plates, respectively, intensity control 150 then is
adjusted to decrease the intensity of the electron beam. As soon as
the light spot on the screen 85 disappears, adjustment of control
150 is terminated. While the borehole tool is in a formation which
presents a good reflective borehole wall and with the cos waveform
removed from the Z axis, potentiometer 164 next is adjusted to
increase the amplitude of the reflection signals applied to the
cathode circuit 80 whereby a desired maximum light spot appears on
the screen 85 when the electron beam is intensified. With this
adjustment, one obtains the proper or desired white-to-black ratio
due to the presence of maximum reflection signals. Next, the
potentiometer 162 is readjusted to increase the peak-to-peak
amplitude of the cos waveform, while at the same time intensity
control 150 is readjusted to decrease the intensity level of the
electron beam to avoid overdriving the electron gun. These final
adjustments give the final white-to-black ratio for the frontside
and backside trace patterns. For example, in obtaining the display
from which the frontside presentation 90a of FIG. 9 is produced,
the final adjustments are made until the backside trace is removed
from the screen and only the frontside trace pattern is
visible.
Instead of completely removing the backside trace patterns, both
sides of the trace patterns could be presented with one side having
a higher intensity than the other side. Such a presentation is
illustrated in FIG. 12. This presentation is obtained in the final
adjustment step by adjusting the potentiometer 162 whereby the
backside trace pattern is visible but has a low intensity on the
screen of the scope. Since the potentiometer 162 controls the
intensity of both the frontside and the backside, the frontside
will have a higher intensity on the screen.
In order to obtain the backside presentation 90b of FIG. 9, switch
160 is moved to contact terminal 170 instead of terminal 161. The
cos waveform then is applied to juncture 165 by way of
potentiometer 162, inverter 171, terminal 170, switch 160, and
resistor 163. Adjustments similar to that described above are
carried out in order to obtain the backside presentation 90b. If
desired, it is to be understood also that a presentation may be
obtained wherein the frontside is shown as well as the backside but
wherein the frontside has a lower intensity on the screen of the
scope than the backside. In addition, it is within the scope of the
present invention to obtain half sections or intensified half
sections of the presentation of FIG. 6 if desired.
As indicated previously, the two presentations of FIG. 9 were
obtained separately at different times. In this respect, the
frontside figure 90a was produced and recorded on one side of
Polaroid film. Subsequently, the film was shifted to the other side
and the backside figure 90b was recorded. In order to record these
presentations simultaneously, a dual gun oscilloscope could be used
or two single gun oscilloscopes could be employed. The latter
embodiment is shown in FIG. 13. The sin and cos functions are
applied to the horizontal and vertical deflection plates of the two
oscilloscopes. In addition, the reflection signals are applied to
the Z axis of each scope. In order to obtain the two half-sectional
presentations, the cos wave is mixed with the reflection signals
and applied to the Z axis of one scope while the inverse of the cos
wave is mixed with the reflection signals and applied to the Z axis
of the other scope. The arcuate trace patterns t.sub.a and t.sub.b
represent corresponding portions s.sub.a and s.sub.b of the
borehole wall. These patterns may be stepped vertically on the
screens with the stepping potentiometer and photographed with two
cameras respectively.
In the production of any of the presentations of the present
invention mentioned above, caliper information about the radius or
diameter of the borehole may be incorporated in each trace pattern
produced whereby the presentations provide information about depth
of fractures, washouts, etc., into the formation. One technique and
system for incorporating caliper information in the trace patterns
is illustrated in FIGS. 14-16. In the above embodiments, the
voltages applied to the vertical and horizontal deflection plates
to produce the elliptical beam sweep may be defined as K.sub.V
acos.theta. and K.sub.H asin.theta., respectively, where K.sub.H
and K.sub.V are the horizontal and vertical gains of the scope and
a is the radius of a circle generated if .DELTA.t = 1 and K.sub.H =
K.sub.V. These voltages may be modified by the factor .DELTA.t
which is representative of the variation in time between the
transmission and reception of acoustic energy as the transducer is
rotated in the borehole. The term .DELTA.t thus represents
variations in the radius of the borehole at each scanning point and
hence gives information about fracture depth, washouts, etc.
Modification of the cos and sin voltages by .DELTA.t thus will
result in the production of a trace pattern which will deviate from
the true elliptical form in accordance with variations of the
radius of the borehole as sensed during each scanning cycle. Such a
trace pattern is shown in dotted form in FIG. 15 and identified by
reference character 84c. Recordation of a plurality of these trace
patterns in side-by-side relationship, as described above, will
form a helical figure which will reflect not only the presence of
fractures and washouts, etc., but also the depth thereof in or out
of the formations from the normal diameter of the borehole.
Referring now to FIGS. 14 and 16, there will be described in more
detail the system for producing the trace patterns 84c of FIG. 15.
The sync pulses and reflection signals are applied to a pulse
shaper 180 which produces a sharp spike for each of these signals.
In FIG. 16B, these spikes are identified as 93a' and 94a',
respectively. The term t in this FIGURE defines the time between
the shaped sync pulse 93a' the shaped reflection signal 94a' for a
borehole of a given diameter. The shaped sync pulses 93a' and
shaped reflection signals 94a' are separated at 181. The shaped
sync pulses then are delayed at 182, as illustrated in FIG. 16C,
and then applied to trigger a bistable multivibrator 183 for the
production of a step waveform illustrated at 184 in FIG. 16D. The
reflection signals are applied to cause the multivibrator to flip
to its other state whereby a square-wave pulse is produced. The
leading edge of the pulse 184 always begins at the same time during
each transducer operating period relative to the shaped sync pulse
93a'. The trailing edge, however, will vary in time dependent upon
the time of reception of reflected acoustic energy and hence the
time of the production of the reflection signal. Thus, the
variation of the time of occurrence of the trailing edge of pulse
184 may be defined at .DELTA.t. The output of multivibrator 183 is
applied to a low-pass filter 185 for the production of a voltage
output (FIG. 16E) whose amplitude varies in accordance with the
variation of .DELTA.t and hence in accordance with the variation of
the radius of the borehole as the subsurface scanning operations
are cyclically carried out. The time constant of the low-pass
filter can be varied depending on the caliper response desired. The
output of the low-pass filter 185 then is applied to multiplying
circuits 186 and 187 which multiply this output with the waveform
functions acos.theta. and asin.theta.. These waveform functions are
obtained in the manner described, for example, in the system of
FIG. 1. The outputs of multiplying circuits 186 and 187 then are
applied to the vertical and horizontal deflection plates of
oscilloscope 81 to produce the loop-shaped beam sweep that contains
information about the variations in the radius or diameter of the
borehole. The reflection signals are applied to the Z axis, as
indicated above, to produce the trace pattern 84c. These patterns
may be stepped vertically with the stepping potentiometer 116 and
photographed with a camera as described in connection with FIG.
1.
In the system of FIG. 14, the shaped sync pulse also is delayed at
190 to a time period which is slightly beyond the expected arrival
time of the reflection signal. The delayed output pulse from delay
circuit 190 is applied to adder 191 and employed to stop or flip
the multivibrator 183 in the event that a reflection signal does
not occur and after multivibrator 183 has been triggered by the
delayed pulse 93a' from circuit 182. The output pulse from delay
circuit 190 does not affect the multivibrator 183 when it is not
producing an output.
In the system of FIG. 14, instead of employing the low-pass filter
185, it may be desirable to employ an alternative arrangement for
producing a voltage representative of .DELTA.t. Such an arrangement
may comprise a sweep generator and a sample and hold circuit, both
of which are controlled by the output from multivibrator 183. The
sweep generator is employed to generate a sawtooth wave voltage at
the start of the pulse from multivibrator 183. This sweep waveform
is simultaneously amplitude sampled and stopped at the occurrence
of a reflection signal. The sampled amplitude then is held for the
remainder of the downhole transducer pulsing period and employed as
.DELTA.t. The cycle is repeated when the downhole transducer again
is pulsed for another operating period and a subsequent amplitude
is sampled and held to obtain a voltage representative of
.DELTA.t.
As a further alternative, half sections of the trace pattern 84c
may be recorded or intensified to aid in interpreting the
presentations produced from data obtained from different angular
sections of the borehole as can be understood from the description
of the system of FIG. 10.
In a further embodiment, opposite sides of each trace pattern
forming the helical configurations may be produced in different
colors to allow the sides of the helix on which the information is
present to be more readily distinguished. In the production of such
presentations, one side of each loop-shaped trace pattern may be
produced in one color, for example, red, while the other side may
be produced in another color, for example, blue. Color film may be
employed to record the trace patterns in the form of a helix. If
the frontside traces and backside traces overlap each other in the
formation of the helix, a purple hue will result when color film is
employed. However, when there is no overlapping of the traces due
to the absence of reflection signals and hence the presence of
fractures, the color will be in red or blue depending upon the side
of the helix on which the fracture is reflected.
Referring to FIG. 17, there will be described a display system for
obtaining trace patterns wherein one side is one color and the
other side is another color. The display system comprises a
cathode-ray tube 200 having a screen 201 capable of displaying
color when irradiated with electrons. Cathode-ray tubes of this
nature are well known in the art and include three electron guns
for emitting three beams of electrons which are focused to
irradiate three corresponding phosphorus spots on the screen when
they are swept by the deflection system. In the present
arrangement, only two guns comprising cathodes 202 and 203 are
employed since it is desired to produce the frontside and backside
of each trace pattern in two colors only. The system shown also
includes a single pair of vertical deflection plates 204 and a
single pair of horizontal deflection plates 205 for concurrently
sweeping the two electron beams. The desired trace patterns are
obtained by applying the cos waveform to the vertical deflection
plates 204 and the sin waveform to the horizontal deflection plates
205. It is to be understood that the gain of the vertical and
horizontal amplifiers (not shown) may be adjusted to obtain the
desired form of the trace patterns. In addition, the cos waveform
is mixed with the reflection signals and applied to the cathode 203
while the inverse of the cos waveform is mixed with the reflection
signals and applied to the cathode 202. As can be understood in
connection with the description of the embodiments of FIGS. 9-12,
one electron beam will be intensified with reflection signals
during the backside sweep, while the other electron beam will be
intensified by reflection signals during the frontside sweep.
Hence, if the cathode 202 is focused to irradiate the red
phosphorus spots while the cathode 203 is focused to irradiate the
blue phosphorus spots, the backside of each trace will be in red
while the frontside will be in blue. The helical configuration may
be obtained by stepping each trace pattern and photographing the
traces with color film.
Although the downhole transducing means 33 was described as a
single transducer for transmitting and receiving acoustic energy,
it is to be understood that a transducing means comprising two
separate transducers could be employed, respectively, for
transmitting and receiving acoustic energy, while rotating, to
obtain the same information as described above. A dual transducer
system is shown in FIG. 18 wherein the transmitter is illustrated
at 206 and the receiver is illustrated at 207. In this system, the
transmitter and receiver are operated and focused to transmit
acoustic energy into the formations for the reception of reflected
energy from interior reflecting surfaces within the formations
spaced from the borehole wall. Thus, the interior of the formations
is cyclically scanned as the transmitter and receiver are rotated.
The reflection signals from the interior reflection surfaces may be
employed to produce three-dimensional figures representative of the
configuration and location of the reflecting surfaces in the
formations. Such a figure or representation is illustrated at 209
in FIG. 19. The smaller cylinder 210 represents the interior of the
borehole, while the oblique surface 211 represents the fracture 91
(FIG. 2) as it exists in the formations. In FIG. 19, the borehole
has been deemphasized while the reflection signals from the
reflection surfaces in the formations have been accentuated.
Referring to FIG. 20, as well as to FIGS. 21 and 22, there will be
described the circuitry employed for obtaining the presentation of
FIG. 19. The oscilloscope 81 is operated as a plan position
indicator. In this respect, an electron beam sweep is produced
which radially moves outward and back from the center of the screen
85 for each transmitter-receiver operating period. The beam sweep
also is rotated whereby each radial sweep begins at a different
angular position. The intensity control 150 of the scope 81 is
adjusted to a level such that the electron beam spot is not visible
on the screen 85 until a reflection signal is applied to the scope.
These reflection signals turn the beam ON at positions on the
screen dependent upon the distance from the transmitter and
receiver to the reflecting surface. The borehole wall reflection
signal is gated out whereby only reflection signals from within the
formations are registered on the screen of the scope. By suitably
adjusting the intensity control, only reflection signals above a
certain level are allowed to intensify the electron beam whereby
background is minimized and the internal reflecting surfaces are
accentuated.
The circuitry for producing the PPI scan comprises two transistors
214 and 215, the outputs of which are applied to the vertical
deflection plates and the horizontal deflection plates,
respectively, of the scope 81. Normally, these transistors are
biased to cutoff. The cos waveform and sin waveform, obtained from
the function generator and integrator system of FIG. 1, are applied
to the transistors 214 and 215, respectively, by way of resistors
216 and 217. The sin waveform is illustrated at 109 in FIG. 21A.
These waveforms are employed to charge the capacitors 218 and 219
during cutoff of the transistors 214 and 215, respectively.
The sync pulse, illustrated at 93a in FIG. 22A and produced during
each downhole pulsing period, is delayed at 220 and then applied to
actuate monostable multivibrator 221 for the production of sharp
pulses illustrated at 222 in FIG. 21B. Each of these pulses 222
turns the transistors ON whereby the capacitors 218 and 219 are
rapidly discharged during the period of each pulse 222. After
discharge, the capacitors 218 and 219 charge, whereby the outputs
of transistors 214 and 215 increase to the value of the cos and sin
waves applied through resistors 216 and 217, respectively. Thus,
within the envelope of the cos and sin waveforms applied to
transistors 214 and 215, sharp sawtooth waveforms are produced
which cause the radial beam sweep to be formed. The sawtooth
waveforms produced within sin wave 109 are illustrated at 223 in
FIG. 21. It will be understood that a great many more sawtooth
waveforms will be produced during each downhole rotating cycle than
shown. The envelopes of the cos and sin waveforms cause the beam
sweep to be rotated whereby the PPI scan is obtained.
The output of the downhole receiver is applied to gate 224, shown
in FIG. 20. This output is illustrated in FIG. 22B and comprises
the reflection signal 94a from the borehole wall and subsequent
reflection signals 94b, 94c, and 94d from reflecting surfaces from
within the formations. The purpose of the gate 224 is to gate out
the reflection signal 94a from the borehole wall while allowing
subsequent reflection signals to pass to the Z axis of the
oscilloscope. In this respect, the delayed sync pulse, illustrated
at 93b in FIG. 22C, triggers a monostable multivibrator 225 which
produces a delayed gating pulse illustrated at 226 in FIG. 22. This
pulse opens the gate 224 after occurrence of the reflection signal
94a whereby only the subsequent reflection signals 94b-94d are
allowed to pass to the Z axis. Although not shown, a time variable
gain may be employed to increase the amplitude of the later
arriving signals.
Since the sync pulse is delayed before multivibrator 221 is
triggered, each radial beam sweep is delayed following the
occurrence of sync pulse 93a. This delay eliminates on the screen
85 the time lag between the production of each downhole acoustic
pulse and the detection of reflected pulses whereby the effect of
the borehole is diminished.
As the transmitter 206 and receiver 207 are rotated and the tool 32
is moved upward during logging operations, a stepping voltage (in
FIG. 20) is applied from the stepping potentiometer 116 in order to
slowly displace upward the resulting displays produced on the
screen 85 as the beam sweep is rotated. The horizontal and vertical
gains of the scope 81 may be adjusted to obtain an elliptically
shaped display on the screen 85 for each downhole rotating cycle.
The camera 115 employing Polaroid film may be employed to
photograph the resulting displays for the production of the
three-dimensional figure or presentation illustrated in FIG. 19.
Thus, instead of a single trace being recorded in the form of a
helix, a rotating surface or area containing information or data
representative of interfaces within the formations is recorded in a
helical manner. In the alternative, half sections of the display of
FIG. 19 may be recorded or intensified as can be understood from
the description of the system of FIG. 10.
Now that the invention has been described, more detail of
alternative equipment which may be used and some of the downhole
and uphole components will be described.
As mentioned above, instead of stepping each trace pattern or
display and photographing the trace patterns or displays in
side-by-side relationship with a film which is held stationary, the
presentations could be obtained by producing each trace pattern or
display for each scanning cycle at the same position on the screen
of the oscilloscope and photographing successive trace patterns or
displays with a camera whose film is driven continuously with
respect to the screen of the oscilloscope in accordance with
movement of the subsurface tool. For example, referring to FIG. 23,
the cos and sin waveforms are applied to the vertical and
horizontal deflection plates of the oscilloscope 81. In addition,
signals which are a function of the subsurface parameters scanned
are applied to the Z axis to intensity modulate the electron beam.
The trace pattern illustrated at 84 is produced in the same
position on the screen 85 for each downhole scanning cycle. It
begins and ends at the same level or height on the screen. A camera
230 having a continuously driven film 231 is employed to obtain the
desired presentations. The film 231 is driven in correlation with
the movement of the tool by sprocket 232 which is driven by gear
reducer 118 and reel 119 as described above. The records obtainable
with the recording system of FIG. 23 are the same as those obtained
with the stepping potentiometer 116 and camera employing stationary
film described above.
Referring to FIG. 24, the rotating switch 56 for producing cyclic
control pulses comprises a rotating arm 54 which contacts terminal
55 once for each rotation of the transducer 33. Terminal 55 is
coupled to a B+ voltage supply. Contact of the arm 54 with the
terminal 55 results in the production of a pulse across resistor
234 and capacitor 235 which is applied by way of cable conductor 61
to the surface. Cyclic control pulses from the rotating switch 56
are employed to generate the sin and cos functions when
investigating cased hole as mentioned above.
Referring to FIG. 25, the downhole pulse generator 44 and the
circuitry 46 of FIG. 1 now will be described. This circuitry
comprises an oscillator 236 which triggers a transmitter circuit
237 to excite the transducer 33. Transmitter crossfeed produced
when the transducer 33 is pulsed is minimized by the use of a
gating circuitry 238 which blocks the crossfeed but passes the
received signals. The output of circuitry 238 is amplified at 239
and applied to a detector circuit 240 which forms the envelope of
the reflected signals received. In order to obtain synch pulses,
the signal produced by the transducer 33, when it fires, is
attenuated to a low level by the combination of capacitor 241 and
the input impedance of amplifier 239 and then is applied to
detector 240 where its envelope is formed.
Referring now to FIG. 26, the uphole system 76 of FIG. 1 for
separating the sync pulses and reflection signals will be
described. The sync pulses are amplified by amplifier 250 and
applied to a sync multivibrator 251. This multivibrator produces a
square-wave pulse of relatively long duration which prevents
spurious signals or receiver signals from coming through during the
time of its production. This square wave is differentiated at 252.
The pulse formed from the leading edge of the square wave is
applied to conductor 135 and employed for sync purposes as
described above. In addition, it is applied to trigger a delay
multivibrator 253. Its square-wave output is differentiated at 254,
and the pulse formed from the trailing edge of the square-wave
output of multivibrator 253 is applied to trigger a gating
multivibrator 255. This multivibrator produces a square-wave pulse
which occurs when the receiver signal is expected. This square-wave
pulse is applied to open a gate 256 whereby the receiver signals,
amplified at 257, pass through the gate 256 to conductor 77 for
application to the Z axis input of the oscilloscope or other
circuitry to obtain the desired trace patterns or data presentation
on the screen of the oscilloscope.
Referring again to FIG. 18, the transmitter 206 and receiver 207
are coupled together mechanically and rotated by shaft 260. Trigger
oscillator 261 and transmitter circuit 262 are employed to fire the
transmitter 206. The output of the oscillator 261 also is applied
to cable conductor 263 and employed for use as the sync pulse. The
receiver output is amplified at 264 and then applied to the
detector circuit 265 for the formation of the reflection signals
which are transmitted uphole by way of conductor 266. In the
operation of the dual transducer system of FIG. 18, the transmitter
and receiver may be rotated at a rate, for example, of 6
revolutions per minute. The transmitter may be operated at a pulse
rate of 100 to 500 pulses per second. The predominant frequency of
each output acoustic pulse may be in the 100-kilocycle range. The
transmitter and receiver are positioned whereby their sensitive
faces are in planes which are perpendicular to parallel lines
extending into the formations. This arrangement is preferable to
increase the sensitivity to reflecting interfaces in the
formations.
In one embodiment, the magnetic north sensing means 50 and
orienting pulse producing means 51 may be of the type described in
U.S. Pat. No. 3,369,626.
The variable diode function generator 100 of FIG. 1 may be of the
type manufacture by Wavetek, San Diego, California, Model No.
114.
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